A review of monoclonal antibodies in COVID-19: Role in immunotherapy,vaccine development and viral detection

2.1 Hyper immune- convalescent plasma for the treatment of COVID-19 infection

Hyper immune plasma and intravenous immunoglobulin infusions are safe and applicable treatments for a broad range of human infections. During outbreaks and the need to get immediate and effective measures, the use of convalescent serum, or plasma, or complete blood continues to grow and should be used under the WHO guidance. Recovering plasma was used in the 2014 Ebola outbreak, which prevailed in West Africa, for its better-quality of survival, relative to the standard therapy [23]. However, the extensive immune deregulation is a major cause for the severity and harmful manifestations of COVID-19, including the cytokine storm syndrome, which is an overexcited immune-inflammatory reaction to an infection, resulting in acute tissues and organs injury [24]. The timing of the therapy with convalescent patients’ plasma is likely to be precarious; if given at the wrong time, to a COVID-19 patient, the immune-plasma could be ineffective, or even inspire/increase a cytokine storm syndrome. Casadevall and Pirofski [25] underline the dangers of the passive usage of convalescent immunoglobulin, which falls into two categories, the serum disease, and the antibody-dependent enhancement of infection. The serum disease is concomitant with the contamination of other blood pathogens, whereas the antibody dependent enhancement theoretically could create antibodies to one strain of coronavirus, and increase the infection to another coronavirus strain [25]. Moreover, Nguyen et al. [26] reports that the restricted usage of the Intravenous Immunoglobulin (IVIG) includes variable specific neutralizing antibody titer(s) against novel pathogens. The use of IVIG in COVID-19 patients may cause immunoglobulins to bind to the Fc γ receptors competitively, preventing the antibody response elicited by the immune complexes triggered by the virus-antibody binding.

In COVID-19 patients, the convalescent plasma can reverse the inflammatory processes and inhibit the consequences of viral infection. The proposed mechanisms of inhibition included the presence of IgM/IgG neutralizing antibodies which have the capability to inhibit the viral entry to the host cells and activate the hosts’ immune system through antibody dependent cellular immunity [27]. Acosta-Ampudia et al. [28], shows that the plasma of recovered COVID-19 patients contains autoantibodies, cytokines and metabolites different in composition from those of the severe symptomatic cases. This profile is responsible for an early and transient hyper immunity known as the cytokine storm, in patients with severe symptomatic infection. This convalescent plasma, at day 28, may increase lymphocytes (T and B cells) post transfusion and reduce rations of IL-6/IFN- γ and IL-6/IL-10. Both hypotheses control the viral infection and may reduce the sever manifestations caused by the SARS-CoV-2.

The use of convalescent plasma has produced promising results for the treatment of the COVID-19 disease, in 2 studies reviewed by Shen et al. [29], and Duan et al. [30]. Despite the promising data of these studies, the use of convalescent plasma has the following concerns:

(1)

Immunoglobulins are not 100% homologous between individuals.

(2)

The viral load in patients is expected to be higher than the Immunoglobulins transferred to them which mean that the patients will need more than one dose.

(3)

The transferred Igs may give negative feedback to the patient’s immune system which may result in the reduction of the Igs that are naturally produced by the patient’s immune system.

(4)

The possible infusion reactions occurring, between the produced antibodies and the transferred antibodies that could cause immune complexes, may lead to kidney inflammation, or other consequences.

(5)

The viral latency.

(6)

The subtypes of immunoglobulins between donor and recipient.

(7)

There is not enough information about the dominant IgA in the mucosal tissue.

All of these limitations for using convalescent plasma of COVID-19 patients, along with its possibility to aggravate the disease, discourage the use of intravenous immunoglobulins (IVIG) [26].

However, Joyner et al. [31], shows that the infusion of convalescent plasma presents only 1.2% overall serious adverse events, 4 hours after transfusion, in 5000 patients ages ranging from 18–97. Their experience provides no signal of toxicity beyond what is expected from using plasma in severely ill patients. Additionally, given the deadly nature of COVID-19 and the large count of critically ill patients, with multiple comorbidities included in their analyses, the mortality rate does not appear to be excessive. Several clinical trials have been lunched and assigned clinical trial numbers, which include phases 1 to 3 and are listed in Esmaeilzadeh and Elahi [19]. Accordingly, the previously mentioned limitations would pave the way to consider monoclonal antibodies for the neutralization of SARS-CoV-2 that can focus on specific target epitopes on viral particles and pose a potential protection and immunotherapy for COVID-19 [32].

Barnes et al. [33] shows that the plasma IgGs isolated and purified from convalescent plasma, of patients recovered from COVID-19, are more potent neutralizers. It targets not only the RBD of the s-protein epitopes but also epitopes of S1A (in the NTD from amino acid 12 to 306) outside the RBD, as opposed to their plasma Fabs counterparts. The epitope mapping of the RBD and S1A of the s-protein that uses the Negative-Stain Electron Microscopy Polyclonal Epitope Mapping (nsEMPEM) and Single-Particle Cryo-Electron Microscopy proved that these sites are not affected by the mutations, commonly occurring in the SARS-CoV-2 isolates. This may pave the way for antibody therapies or vaccine development.

2.2 Therapeutic monoclonal antibodies targeting SARS-CoV-2

Pharmaceutical companies are in favor to produce monoclonal antibodies as a treatment for COVID-19 including Celltrion, AstraZeneca and Regeneron. The first human study to treat COVID-19 is, using LY-CoV555 neutralizing mAb against the spike protein, and is currently in progress, in phase II trial and is carried out by the pharmaceutical company “Lilly”. The neutralizing antibody LY-CoV555 with a dose of 2800 mg, appeared to accelerate the natural decline in viral load over time, whereas the other doses (700 mg, or 7000 mg) have not [34]. Recently, Bamlanivimab and Casirivimab-Imdevimab are novel virus-neutralizing monoclonal antibodies authorized to treat mild to moderate COVID-19 infected outpatients who are at a risk for progression to a severe level of infection. Also, early treatment may show efficacy in reducing progression in severely infected cases [32]. However, the U.S. Food and Drug Administration issued an emergency use authorization (EUA) for Casirivimab and Imdevimab (Regeneron Pharmaceuticals Inc, https://www.regeneron.com/casirivimab-imdevimab) to be administered together for the treatment of mild to moderate COVID-19 infection in adults and pediatric patients (https://www.fda.gov/news-events/press-announcements/coronavirus-covid-19-update-fda-authorizes-monoclonal-antibodies-treatment-covid-19).

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The neutralizing therapeutic antibodies and vaccine development, which are the potential counter measures controlling SARS-CoV-2 that cause COVID-19 disease, reports that the high dose vs. low dose viral infection of SARS-CoV-2 may affect the lymphocytic immune reactions. The high dose viral exposure belongs to the cases of health-care workers and individuals, who have currently sick or have asymptomatic family members spreading the virus. The low dose viral infection may lead to the stimulation response of the T and B cell lymphocytes, as well as the production of neutralizing antibodies and rapid viral clearance (spontaneous clearance). Whereas the high dose viral infection could cause the increase of the severity of the disease and late viral clearance. This may be due to lymphopenia leading to the ineffectiveness of the T and B cell, then the initiation of the cytokine storm and tissue damage [35]. So generally, the low viral dose is a better candidate for the vaccine; especially if it stimulates cellular immunity and humoral immunity, particularly concerning the production of the neutralizing antibodies. These neutralizing antibodies have the capability to bind to the viral particles, eliminating any free viral particle that can infect the target cells. In other words, these neutralizing antibodies binds with the Angiotensin Converting receptor 2 (ACE2) preventing the binding of the virus particles with the target cells, which in-turn can prevent intracellular replication and viral assembly, as well as viral transmission from cell to cell. So, if we have these neutralizing antibodies based on the neutralizing assays, we can determine the neutralizing epitope and use it as a candidate vaccine (Fig. 3b).

Both human monoclonal antibodies, from hybridoma technology, and plasma of convalescent COVID-19 patients are encouraging immunological strategies for the development of immunotherapy for COVID-19 infection. Recently, Begum and Ray [36] suggested that using B cell lymphocytes producing antibody isolates from convalescent SARS-CoV-2 individuals, for the generation of human B cell hybridomas, and a mixture of human mAbs, for multiple immunogenic targets of SARS-CoV-2 spike protein, might deliver an antibody mix for a long-term treatment therapy with a convalescent focus. Neutralizing monoclonal antibodies bond exactly on the neutralizing epitopes, on the spike protein of SARS-CoV-2, as opposed to the widespread variety of antibodies in plasma. Some plasma antibodies will be neutralizing ones, but many others are non-neutralizing (off-target effects), potentially causing tissue injury. For example, a non-neutralizing antibody binding to a non-spike protein viral antigen could result in a damaging antibody reactions (type I-III) and antibody dependent disease development. These conflicting properties are less likely to occur with the use of a single or combined monoclonal antibodies, which are presently in the initial clinical trials phase [37]. Interestingly, the availability of both non-neutralizing and neutralizing monoclonal antibodies generated in this study will enable the assessment of the S protein immunogens, for the presentation of neutralizing and non-neutralizing epitopes, and inspire effective candidates for vaccine design. The design of an immunogen that improves the quality of mAbs, elicited by natural infection, may well appear as an essential target for vaccine research.

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Scientists have issued papers of specific therapeutic human monoclonal antibodies (hmAbs) (B38, H4, 47D11) targeting SARS-CoV-2 with the prospect that these antibodies are effective. Heavy and light-chains of both B38 and H4 hmAbs which are generated in Nicotiana benthamiana plant leaves show specific binding to the SARS-CoV-2 RBD and in-vitro efficient neutralization capacity [38]. However, ACE2 is an endogenous membrane protein that assists in the infection of SARS-CoV-2. During COVID-19 infection, the extracellular peptidase domain of ACE2, blocks the receptor binding domain (RBD), of the spike protein of SARS-CoV-2. The sole focus of scientists is to produce mAbs targeting the S protein and RBD. Several studies, in vivo, demonstrates the high neutralizing potency of the antibodies targeting these epitopes against SARS-CoV-2 [39, 40, 41]. Other work was conducted to isolate mAbs from memory B cells that were sorted from PBMCs of convalescent patients, who recovered from infection [42].

Separation of B cells from convalescent COVID-19 patients, the collection of B cells that are efficient for generating the needed neutralizing antibodies and the cloning of the neutralizing monoclonal antibodies are labor-intensive tasks. Chi and his colleagues [42] were able to prove that antibodies raised against epitopes, other than RBD, would neutralize the virus. They identified a neutralizing mAb named 4A8 which recognizes an epitope of the N-Terminal Domain (NTD) on the spike glycoprotein. This antibody shows the capacity to neutralize the SARS-CoV-2 virus either in authentic or pseudo-forms. However, the 4A8 antibody fails to recognize the RBD. Almost all generated mAbs, that are targeting the S protein epitope (s), are in the clinical trials, either single, such as, the REGN10933, LY3819253, CT-P59, BRII-198, or combined, such as, LY3819253+LY3832479, REGN10933+REGN10987, AZD8895+AZD1061 [43]. Other mAbs are with the nucleotide analog that blocks the viral RNA polymerase named Remdesivir, such as, the LY3819253.

Another challenge in the development of mAbs is the possible mutations in the S glycoprotein of the SARS-CoV-2 virus. These mutations would affect the neutralizing capacity of an antibody leading to the escape of the variant. Korber et al. [44], identified 14 mutation points in the S protein targeted by all mAbs in the clinical trials. All these mutations are rare, or of low frequency except for one mutation; D614G (outside the RBD) which affects the stabilization of the interprotomer that is found in 3577 counts globally and may suggest a role in human-to human viral transmission. Now, this variant constitutes over 97% of the isolates globally [45] and may cause a conformational shift in the S protein due to the interruption occurring between S1 and S2 contacts. In 9 countries, different counts of mutations are discovered, such as 8 in Europe and 65 in the USA. Interestingly, Yurkovetskiy et al. [45] tested human mAb with the D614G mutation and concluded that it could not affect the antibodies targeting the RBD to cause the blockage of the ACE2 binding with the RBD. During infection, the host proteases cleave the S protein on the S1 (N-terminal) and the S2 (C-terminal) subunits. The S1 contains the signal peptide NTD and RBD, whereas the S2 subunit contains the heptad repeats (HR) 1 and 2, which are necessary membrane components. These 2 repeats have been fused and nominated, also as potential candidates, to block viral fusion based on the data of 1A9 monoclonal antibody against SARS-CoV HR2 domain [46].

The hypothesis of using this antibody against SARS-CoV-2 is based on the fact that the S2 protein is highly conserved. Figure 4, created with BioRender.com, shows the potential promise of the monoclonal antibodies against the spike epitopes of SARS-CoV-2.